Magnetic RAM

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					     Magnetic RAM
a.k.a Magnetoresistive Random Access Memory




         By: Ashley Jefferson
     What is Magnetic RAM?

MRAM is memory technology that uses electron
spin to store information

Unlike conventional RAM chip technologies, data
is not stored as electric charge or current flows, but
by magnetic storage elements.
        Magnetic RAM Architecture
                    Shows how MRAM reads and writes




Credit: http://domino.research.ibm.com
  What is Magnetic RAM? How
          does it work?
 An MRAM chip is made up of millions of pairs of tiny
  ferromagnetic plates (like the one covering hard drives)
  called memory cells, i.e., magnetic sandwiches consisting
  of two magnetic layers separated by a very thin insulating
  layer

 One of the two plates is a permanent magnet set to a
  particular polarity, the other's field will change to match
  that of an external field. A memory device is built from a
  grid of such "cells".
An image of the layers involved
 in an MRAM storage device.




Credit: http://domino.research.ibm.com
         How does it work?
 MRAM works like the read/write head of a
  hard drive.

 But unlike a hard drive, which includes
  mechanical parts (the moving arm holding
  the read/write head and the rotating plates
  on which the information is stored), MRAM
  is a solid state device and, as such, has
  much greater speed and durability
             How does it Read?
 An MRAM chip reads information by measuring the
  electrical resistance of a specific cell that, in turn,
  depends upon the alignment of the magnetic moments
  of the layers of the cell.

 To read a bit of information, a current is passed
  through the memory cell.

 If the magnetic moments are in a parallel orientation,
  then the detected resistance would be smaller than if
  they were in an anti-parallel orientation.
           Diagram of Read Process




Credit: http://www.tfot.info/
           How does it Write?
 Write is achieved by the alignment of the magnetic
  moments of the two memory layers into one or the
  other relative orientation.

 Current is passed through two sets of parallel wires
  or write lines (called a bit line and a digit or word
  line), which pass over and beneath the memory
  cells, respectively

 To write to a particular memory cell (bit), current
  is passed through the two wires that intersect at
  that memory cell.
           Diagram of Write Process




Credit: http://www.tfot.info/
 Advantages of Magnetic RAM
 MRAM has been called the “ideal memory”-
  potentially combining the density of DRAM with the
  speed of SRAM and non-volatility of Flash memory
  or hard disk, and all the while consuming a very low
  amount of energy

 MRAM has much faster write speeds than Flash and
  has an unlimited endurance, meaning that MRAM is
  not subject to the degradation suffered by Flash.
        Advantages of MRAM
 MRAM can resist high radiation, and can operate in
  extreme temperature conditions. It is likely that we’ll
  see the first MRAM in applications that need such
  properties

 Like Flash, MRAM retains data after a power supply
  is cut off, potentially eliminating that seemingly
  endless boot time of conventional computers when
  data from the hard drive is transferred to RAM, as
  well as loss of data when the computer is suddenly
  shut off.
        Advantages of MRAM
 The magnetic architecture of the chip can be
  reprogrammed on a whim and its adaptability could
  make it very popular with manufacturers of special-
  purpose computing hardware, from video-game
  platforms to medical diagnostic equipment.

 The chip's nanomagnets -- on the order of 110
  nanometers wide -- can be assembled into arrays that
  mirror the function of transistor-based logic gates in
  addition to storing information. These logic gates are
  the building blocks of computer technology, giving
  microchips the power to process the endless rivers of
  binary code.
        Advantages of MRAM
 Using a magnetic state for storage has two main
  benefits:
   – 1) the magnetic polarization does not leak away with
     time like charge does, so the information is stored
     even when the power is turned off; and
   – 2) switching the magnetic polarization between the
     two states does not involve actual movement of
     electrons or atoms and thus has no known wear-out
     mechanism.
 Disadvantages of Magnetic RAM

 Is (currently) expensive
 Power consumption of MRAM technology
  is still high
 Freescale’s MRAM technology only holds
  4M. So it can’t currently be widely used
                  Comparison Table




Credit: http://www.tfot.info/
   What is MRAM going to be
            used for?
 Proposed uses for MRAM include devices such
  as:
  – Aerospace and military systems
  – Digital Cameras
  – Notebooks
  – Smart Cards
  – Mobile Telephones
  – Cellular base stations
  – Personal Computers
             Is it available today?
 Although MRAM has many advantages over virtually every existing
  memory type, it is still in its infancy.

 Many had hoped MRAM would usher in the age of instant-on
  computers able to replace the computer main memory and hard
  drives, but, due mainly to its cost, these hopes remain a dream

 Even though many large companies such as IBM, Intel and HP, are
  working on MRAM, Only two vendors have succeeded in bringing
  MRAM parts to the mass market - Cypress and Freescale.

 Cypress, however, has discontinued their offering shortly after
  release
            Is it available today?
 In February, Toshiba and NEC announced a 16 Mbit MRAM
  chip with a new "power-forking" design. It achieves a transfer
  rate of 200 MB/s, with a 34 ns cycle time - the best
  performance of any MRAM chip. It also boasts the smallest
  physical size in its class -- 78.5 square millimeters -- and a low
  power requirement of 1.8 volts.

 In July 2006, Freescale started selling the first commercial
  MRAM module, with 4Mbit of memory, for $25 a piece.

 This is still very expensive and low density, and probably suits
  a very small list of select customers. A realistic timeframe for a
  cell phone with MRAM or a MRAM-Disk-On-Key is probably
  2010 at least.

				
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